The reinforcing of cement with different types of fibers is well known. The advantages obtained by stengthening a mineral material in order to confer ductility and greater tensile resistance thereon has been long known, as is evident from the ancient existence of daub or reinforced concrete.
Similarly, attempts have been made from quite early on to reinforce cement with fibers. The industrial use of asbestos fibers as a reinforcement, for example, dates from the beginning of the twentieth century.
However, and particularly since the discovery in the 1960's of the increased risks of cancer due to touching and inhaling asbestos fibers, other types of fibers for reinforcing cement have also been utilized. In this respect, steel fibers, cast iron fibers, glass fibers, cellulose fibers, polypropylene fibers and other synthetic fibers, natural jute and bambou fibers, etc. have been used. However, the use of fibers of these types has not developed satisfactorily, because such cement fiber mixtures are difficult to manufacture.
On this account, the known processes of the prior art which employed means of filtration, impregnation, projection, or mixing the fibers with cement when the cement is mixed (a process known as PREMIX) each has disadvantages which limit the use thereof. For example, the process of manufacturing the cement-fiber mixture by filtering the cement through fibers is not suitable for all types of fibers. These fibers must be quite thin in order to form an efficient filter and have a sufficient affinity with water, which excludes, in particular, the use of glass fibers. Furthermore, the need to press the manufactured parts excludes the production of high relief parts. Moreover, a circuit for supplying and eliminating the water used at the filtering stage is necessary, a step which involves high expenditure.
The process for manufacturing the cement fiber mixture by means of impregnation is time consuming and difficult to carry out, therefore it is expensive.
The manufacture of a mixture of cement and fibers by spraying the cement and fibers onto a mold or a wall is not suitable for all types of fibers, as with the manufacturing process by means of filtration. The fibers must have properties of size and appearance which enable them to be sprayed, and thus requires expensive fibers which must be manufactured in a particular way.
The spraying of the cement paste requires that large quantities of water are used, hence there are aging problems associated with the product obtained by this process, i.e., the properties deteriorate over time. Furthermore, because the projection method is complicated to carry out, it requires a trained and qualified operator.
Finally, the prior art process of mixing the fibers with the cement when the cement is mixed (a process known as PREMIX), considerably limits the proportion of fibers that can be mixed with the cement paste. The increase in the viscosity of the mixture due to the addition of fibers must generally be compensated for by initially using a larger amount of water. Therefore, PREMIX results in a product which exhibits inferior performance over time, similar to the disadvantage of the manufacturing process by spraying. Also, as with the manufacturing process by means of spraying, the labor force carrying out the PREMIX process must be trained and qualified, which renders the methods known as the PREMIX type expensive and essentially limited to small scale production.